Gerard Ahern PhD, the study’s senior investigator and associate professor in the Georgetown’s Department of Pharmacology and Physiology, explained that it is well known that sunlight provides vitamin D. It is suggested that, among other things, vitamin D has an impact on immunity. Ahern’s team has found a completely separate role of sunlight on immunity. He added that some of the benefits of immunity attributed to vitamin D might in fact be due to this new mechanism.

In a finding that marks the first reported human cell responding to sunlight by speeding its pace, the team found that low levels of blue light found in the sun’s rays makes T cells speed up. Ahern notes that whether T cells are killers or helpers, they need to move to the site of an infection and orchestrate a response to do their work.

The study demonstrates that sunlight triggers key immune cells directly by increasing their movement. Ahern added that while production of vitamin D requires UV light, the same UV light could promote skin cancer and melanoma. On the other hand, blue light from the sun, as well as from special lamps, is safer.

Although the human T cells that were studied in the laboratory were isolated from mouse cell culture and from human blood, and were not specifically skin T cells, human skin has a large population of T cells – about twice the number of that circulating in the blood. It is known that blue light can reach the second layer of the skin (the dermis) and that the dermis’ T cells can move throughout the body.

The researchers traced the molecular pathway activated by the light, thereby decoding how blue light makes T cells move. They found that hydrogen peroxide was synthesized and this drove the motility response in T cells by activating a signaling pathway that increases T cell movement. White blood cells release hydrogen peroxide when they sense an infection. The hydrogen peroxide is used to “call” T cells and other immune cells to mount an immune response and to kill bacteria.

For Ahern, everything fits together. It is known that an immune response uses hydrogen peroxide to make T cells move to the damage, and now they’ve found that sunlight produces hydrogen peroxide in T cells, which makes the cells move.

Ahern understands that there is much work to do to analyze these findings fully, but suggests that if blue light T cell activation only has beneficial effects, it might be possible to offer blue light therapy to boost patients’ immunity systems.